The present invention relates to the fabrication of integrated circuitry and, more particularly, to forming a layer of material within and about a cavity in a surface of a substrate.
There generally are many steps associated with fabricating integrated circuitry. Some of these steps require forming a layer of material within and about a cavity in a surface of a substrate. In this connection, it is not unusual in very large scale integration to provide isolation trenches between areas of a substrate on which differing parts of an integrated circuit are to be formed. Such trenches physically and electrically isolate the areas. In general, each isolation trench includes not only a physical trench-like cavity within the substrate, but also a filling within the cavity of an insulating material, such as a silicon dioxide. The trench is filled with the insulating material by forming a layer of the same on the substrate surface within and about the same. One way of forming the layer is to deposit the material in a deposition chamber from a gas which contains constituents of the desired insulating material. For example, if the insulating material is silicon dioxide, it can be deposited by low pressure chemical vapor deposition of silicon and oxygen species from tetraethoxysilane (TEOS).
The conventional practice is to maintain the gas from which the insulating material deposits at a generally constant pressure within the deposition chamber. As discussed below, this is a relatively high pressure in view of the necessity of being reasonably sure that the trench fills even though the configuration of the same, i.e., the ratio of the depth of the trench to its width (its minimum opening width) changes during the formation of the filling layer. This ratio is typically referred to as the aspect ratio. That is, as also discussed below, it will be seen that as the deposition progresses, this aspect ratio changes dramatically--as the layer is formed, the width of the opening narrows dramatically relative to the depth of the trench. That is, in order to effectively fill the trench, molecules have to be able to penetrate the trench and make their way to the bottom without incurring heavy losses due to reactions with the side walls.
While increase in pressure has a beneficial effect on trench filling capacity in view of this problem, it has the unfortunate adverse effect of particle generation. That is, as pressure increases more particles are generated due to an increase in gas-phase reaction rates.